Bridges and some roadways in modern countries throughout the world are frequently formed, in part, of concrete reinforced with steel. The supporting steel or other subsurface materials provide the strength needed for the overlying road surface to enable it to carry the massive weight loads of vehicles, trains and the like. Such roadways are found on soil or over the bridged rivers and canyons or simply on city and state streets.
The employment of metal reinforcement such as steel in the underlying concrete material supporting an overlying roadway provides support to the roadway. The metal reinforcing material such as reinforcing bar (a.k.a. rebar) or wire mesh, when engaged within concrete road surfaces or support surfaces, produces a structural material that exceeds the strength of either material if employed individually in the same sized structure. This hidden underlying support technology, provided by metal reinforcing material, has enabled roadways to withstand much higher weights for much longer periods than would be possible in an unreinforced roadway surface.
However in many industrialized countries, concrete infrastructure is aging rapidly. Roads, bridges, parking structures, airport facilities, and marine structures are impacted and show in many cases severe signs of degradation. One of the most important causes of the premature deterioration of concrete is the exposure to chlorides found in de-icing salts and seawater, which, upon penetration in the concrete cover, ultimately initiates the rebar corrosion process. Other types of degradation affect concrete structures, such as freezing and thawing damage, alkali-silica reaction (ASR), and exposure to acidic environments. In the United States only, it has been reported that more than two thirds of the six hundred thousand bridges are more than 25 years old, and thus likely to require serious maintenance. For additional information regarding this, the reader is invited to refer to FHWA—2010 Status of the Nation's Highways, Bridges, and Transit—Condition & Performance. Technical report, Report to congress, 2010—Exhibit 3-20 and Y. H. Huang, Adams T. M., and Pincheira J. A. “Analysis of life-cycle maintenance strategies for concrete bridge decks”, Journal of Bridge Engineering, 9:250-258, 2004. The contents of the aforementioned document are incorporated herein by reference. According to various sources, between 34% of bridges older than 25 year old are structurally deficient or functionally obsolete. It has been estimated by some that it would cost approximately US $70-$90 billion to repair these structures, where about 20% of this cost would be directly due to corrosion. For additional information regarding this, the reader is invited to refer to Y. Liu et al., “Modeling the time-to-corrosion cracking in chloride contaminated reinforced concrete structures”, ACI Materials Journal, 95:675-681, 1998 and T. J. Kirkpatrick et al. “Impact of specification changes on chloride-induced corrosion service life of bridge decks”, Cement and Concrete Research, 32:1189-1197, 2002. The contents of the aforementioned documents are incorporated herein by reference.
For owners and managers, decaying reinforced concrete structures not only represent a major safety issue but also impose a growing financial burden at a time of unprecedented budget restrictions.
In light of the above, it is becoming increasingly important to find cost-effective solutions to improve the design of new concrete structures and optimize the maintenance of existing structures. The construction industry has clearly identified the urgent need for the accelerated development and introduction of innovative new technologies and processes to ensure the quality, durability, efficiency, and sustainability of infrastructure systems as well as support sound asset management and decision-making.
While the construction industry is clearly in need of life-cycle cost analysis tools that explicitly take into account the impact of material degradation, few suitable solutions are currently available. In particular, most available solutions for assessing the degradation of concrete structures and planning maintenance of such structures rely on the practical experience of structural engineers and on visual inspection. As such, the reliability of such solutions is highly dependent on the individual skills of those conducting the analysis and planning activities, which is inefficient and may not always result in concrete structures being properly managed and their safety being ensured.
Some numerical tools have been suggested for quantifying and predicting the long-term durability of concrete structures. Probabilistic approaches have also received attention recently. It is widely acknowledged that concrete, as a material, is inherently variable due to its heterogeneous composition of aggregates of multiple scales and casting techniques which introduce local variations in compositions of paste, water, and aggregate content. Furthermore, concrete structures are exposed to highly variable environmental conditions, which add to the need of using probabilistic concepts in the analysis.
However, conventional probabilistic methods used for quantifying and predicting the long-term durability of concrete structures generally fail to suitably consider the local variations in the properties of the concrete structures and fail to provide suitable mechanisms for taking into account local variations in degradation.
Against the background described above, there is a need in the industry to provide solutions for estimating and predicting degradation and durability characteristics of concrete structures that address at least some of the deficiencies of existing solutions and that can be used to assist in planning maintenance activities related to concrete structures.